1. Field of the Invention
The present invention relates to hand tools, such as those used to make coarse and fine adjustments on electrical or mechanical apparatus, for example, trimming potentiometers or the carburetor of an internal combustion engine.
2. Description of the Prior Art
Hitherto to make fine adjustments possible on such apparatus, it has been the practice to build into each apparatus, such as the aforementioned potentiometer, a reduction gear which reduces the rotation of an adjusting element in the apparatus sufficiently for fine variations to be effected in the setting of the apparatus. This may require a substantial number of turns of the hand tool to arrive at a coarse setting from which final fine adjustments can be made. On electrical and electronic apparatus where there are often several trimming potentiometers to be adjusted to final optimum settings before selling the apparatus or putting it into operation, adjustment of the potentiometers can take a considerable time.
A screwdriver has been proposed which can be used in the normal way and which has a reduction gear coupling a knob mounted at one end of the handle of the screwdriver to the blade projecting from the other end. By holding the handle of the screwdriver with one hand and rotating the knob with the other, the blade is made to rotate through a small angle for several turns of the knob. However, the reduction gear within this screwdriver requires precision engineering in manufacture and does not readily lend itself to inexpensive and easy production. It comprises two epicyclic gears in tandem, each gear being in the form of a cage holding planets consisting of steel balls engaging a circumferential groove in a spindle acting as the sun wheel. The cage of one gear is connected to the sun wheel of the next and threaded adjusting means are provided whereby the balls can be sufficiently urged into adequate frictional engagement with the grooves. Such a tool has the advantage, however, of enabling apparatus such as trimming potentiometers to be manufactured without the embodiment of means for enabling fine adjustments to be made.